Inhibiting compound



252. COMPOSITIONS,

Patented Nov. 5, 1929 UNITED STATES LAIIIHIv PATENT OFFICE LUD'WIG J.GHRISTMANN, OF JERSEY CITY, NEW JERSEY, ASSIGNOR TO AMERICAN CYANAIIDCOMPANY, OF NEW YORK, N. Y., A CORPORATION OF MAINE INHIBITING COMPOUNDNo Drawing.

This invention relates to methods of cleaning or pickling metals bysubjecting the same to an acid bath.

In the metal industries, particularly in the manufacture of iron orsteel sheets or the like, which are to be coated with protective metalssuch as tin, zinc or cadmium, it is a common expedient to first cleanthe metal surface in order that the subsequent coating material mayadhere firmly thereto, without danger of peeling off of the coating.This cleaning treatment usually consists in providing a dilute solutionof a non-oxidizing mineral acid material, such as sulphuric acid, calleda ickling bath, and immersing the metal art cles to be cleaned in thebath for a length of time sufiicient to remove scale, oxide and othermatter from the surface of the metal. The bath is usually maintained ata predetermined temperature, usually above room temperature, during thepickling operation.

The acid in the pickling bath not only acts to remove the undesirablesurface materials but also tends to attack the metal itself and, toprotect the metal from attack by the acid, there is usually added to thepickling bath a small amount of a substance called an inhibitor. Theinhibitor permits the acid to remove the undesirable surface materialfrom the metal and prevents, either in whole or in part, the action ofthe acid upon the metal itself. Ordinarily, in the absence of aninhibitor, the acid in attacking the metal gives oil a substantialquantity of hydrogen or other gaseous substances with the production ofan acid mist or spray which is injurious to the workmen and, inaddition, results in appreciable loss of acid.

The present invention is intended to provide an inhibitor which may beprepared easily, which is low in cost and which is highly effective in apickling bath even though present in small amounts.

I have discovered that a condensation producppf o-toluidine and sulfurchloride is highly effective as an inhibitdfiii' apickling bath. Thismaterial may be obtained in any suitable and well known manner. For in-Application filed September 18, 1929. Serial No. 393,591.

stance, one method of preparing my inhibitor is as follows:

One mol. of dry o-toluidine hydrochloride is made into a slurry withbenzol and this mixture is poured into a suitable container fitted witha thermometer, a reflux condenser and an efiicient stirrer. Six mols. ofsulfur chloride (S Cl are quickly added and the mixture warmed on asteam bath to 60-7 0 C. with stirring until the reaction is complete.When a sample of the reaction mixture can no longer be di-azotized orcoupled it is considered to be complete. The di-azotization test iscarried out in the usual manner with sodium nitrite and B-naphthol. Thereaction mixture is filtered and the filter cake washed with benzol,reslurrying with additional benzol if necessary to wash out excesssulfur chloride. The material may then be dried.

The inhibitor constituting the subject matter of my invention was testedin a pickling bath in the following manner:

A pickling solution was prepared consisting of 250 cc. of dilutesulfuric acid containing 8% by weight of 66 B. acid. The solution wasplaced in a suitable vessel, maintained at a temperature of 183-185 F.and 0.100 grams of condensation product of o-toluidine and sulfurchloride was added to the solution. This is equivalent to about 4one-hundredths of one percent of inhibitor in the bath.

Strips 3 long and 4" wide'of 30 gauge tin plate stock were used for thetests. The specimens were first cleaned with ether to remove any oil orgrease on the surface, and, after drying were immersed in the picklingbath for five minutes to remove the oxide scale. The specimens wereremoved from the bath, dried and weighed. The specimens were immediatelyreturned to the pickling bath, immersed for twenty minutes, washed,dried and weighed again. The loss in weight was determined and thespecimens were subjected to another 20 minute test. Throughout thetests, check runs were made with similar pickling baths but withoutusing any inhibitor. The table given below shows the results obtainedwith and without the condensation product of o-toluidine and sulfurchloride in the pickling bath From the above it is clear that thecondensation product of o-toluidine and sulfur chloride is a goodinhibitor and effectively curtails the action of the acid upon themetal. This is particularly true in view of the fact that the samplepickled in the bath containing no inhibitor was so rapidly dissolved inthe acid that before the end of forty minutes it was completely insolution. Therefore, no effort was made to weigh the check samplesduring the tests. In similar tests carried out at higher and lowertemperatures, it was found that this inhibitor was equally effective asat temperatures originally described.

Although I have described my invention in some detail, it is not limitedto the specific matters set forth. The amounts of inhibitor used inpickling baths may, of course, be varied widely and the nature of thebath may also be changed to suit any particular conditions which mayprevail. In general, it is not necessary to use more than 1% ofinhibitor in the bath and for most purposes less than 0.1% issuflicient. It is to be understood that my invention is not to belimited except as set forth in the claims appended hereto.

I claim 1. A method of cleaning or pickling metals which comprisessubjecting the same to a pickling or cleaning bath containing a smallamount of a condensation product of o-toluidine and sulfur chloride.

2. A method of cleaning or pickling metals which comprises subjectingthe same to a pickling bath containing less than 1% of a condensationproduct of o-toluidine and sulfur chloride.

3. A method of cleaning or pickling metals which comprises subjectingthe same to a pickling or cleaning bath containing less than 0.1% of acondensation product of o-toluidine and sulfur chloride.

4. A method of cleaning or pickling metals which comprises subjectingthe same to a. pickling or cleaning bath containing about 0.01% of acondensation product of o-toluidine and sulfur chloride.

5. A bath for pickling metals comprising a non-oxidizing mineral acidand a small amount of a condensation product of o-toluidine and sulfurchloride.

6. A bath for pickling metals comprising a. non-oxidizing mineral acidand less than 1%

